US 6937179 B1 Resumen A resistor tuning network is disclosed that comprises a first resistor connected in parallel with a second variable resistor and a third resistor coupled in series with the first resistor and the second variable resistor. The second variable resistor comprises an R-2R ladder network having an input and first and second output terminals, with a first line having a plurality of first arms connected in series with the input and first output terminal and nodes between each pair of arms, each arm having an identical resistor R. A series of shunt arms, each with a 2R resistor and a switch, are selectively connected between the respective nodes and the first or second output terminal. The resistance of the resistor tuning network is tuned by varying the switch positions in the shunt arms in the R-2R ladder network.
Reclamaciones(22) 1. A resistor tuning network comprising:
a first resistor having a fixed value of resistance R
1, said first resistor having an input and an output; a resistor ladder network having a variable value of resistance R
2, said resistor ladder network connected between the input and the output of the first resistor in parallel with the first resistor, said resistor ladder network having an input and first and second output terminals, said first output terminal of said resistor ladder network being connected to said output of said first resistor; wherein said resistor ladder network comprises a first line comprising a plurality of first arms connected in series with the input of the resistor ladder network and the first output terminal of the resistor ladder network and nodes between each pair of arms, each arm having an identical resistor R, and a second line connected to said first output terminal of said resistor ladder network, and a third line connected to said second output terminal of said resistor ladder network;
a series of shunt arms, each shunt arm having a first end connected to a respective node and a second end, a resistor which has a value which is a multiple of R and a switch in series between the first and second end of each shunt arm, each switch having a first, closed position connecting the shunt arm to the second line and a second, open position connecting the shunt arm to the third line, such that the resistance of the resistor ladder network is varied dependent on the switch positions and is at a maximum value when all switches are open and at a minimum value when all switches are closed, whereby a resistance can be tuned by varying the switch positions in the resistor ladder network; and
a third resistor having a fixed value of resistance R
3, said third resistor connected in series with the parallel connected first resistor and resistor ladder network; wherein said resistor tuning network operates as a tunable resistor by providing variable output values of resistance when said switch positions in said resistor ladder network are varied.
2. The resistor tuning network as claimed in
where V
_{IN }is the input voltage to the resistor tuning network, I_{OUT }is the output voltage of the resistor tuning network, R1 is the value of resistance of the first resistor connected in parallel with the R-2R resistor ladder network, R2 is the resistance of the R-2R resistor ladder network, R3 is the value of resistance of the third resistance coupled in series with the parallel connected first resistor and resistor ladder network, and the letter b represents a tuning variable that represents a current switch position where the tuning variable b is equal to 2^{n }divided by a setting parameter, wherein the setting parameter varies between 1 and 2^{n }in unit increments where n is the total number of shunt arms.3. The resistor tuning network as claimed in
4. The resistor tuning network as claimed in
5. The resistor tuning network as claimed in
6. The resistor tuning network as claimed in
7. The resistor tuning network as claimed in
8. The resistor tuning network as claimed in
9. The resistor tuning network as claimed in
10. The resistor tuning network as claimed in
11. The resistor tuning network as claimed in
12. A method of operating a resistor tuning network as a tunable resistor, said method comprising the steps of:
providing a first resistor having a fixed value of resistance R
1; providing a resistor ladder network that comprises an R-xR ladder, where xR is a multiple of R, where R is the value of resistance of resistor R in said resistor ladder network, said resistor ladder network having a variable value of resistance R
2; connecting said resistor ladder network in parallel with said first resistor;
varying the resistance of the R-xR ladder network by selectively opening and closing switches connected in xR branches of the R-xR ladder network to connect lesser or greater numbers of the xR branches to an output terminal of the R-xR ladder network in order to create a desired tuned resistance value of said R-xR resistor ladder network; and
connecting an input of said R-xR ladder network in series with a third resistor of said resistor tuning network, said third resistor having a fixed resistance R
3; and varying said switch positions in said resistor ladder network to provide variable output values of resistance for said resistor tuning network.
13. The method as claimed in
where V
_{IN }is the input voltage to the resistor tuning network, I_{OUT }is the output voltage of the resistor tuning network, where R1 is the resistance of the first resistor connected in parallel with the R-2R ladder network, R2 is the value of resistance of the R-2R ladder network, R3 is the value of resistance of the third resistor, and the letter b represents a tuning variable that represents a current switch position where the tuning variable b is equal to 2^{n }divided by a setting parameter, wherein the setting parameter varies between 1 and 2^{n }in unit increments where n is the total number of shunt-arms in said R-2R ladder network.14. The method as claimed in
providing a tunable resistor in an electronic component on an integrated circuit chip wherein said tunable resistor comprises said resistor tuning network.
15. The method as claimed in
16. The method as claimed in
tuning said transfer function of said resistor tuning network by a control signal, wherein said control signal is capable of selecting one of a plurality of said switch positions in said resistor ladder network of said resistor tuning network.
17. The method as claimed in
maintaining resistor ratios in said transfer function of said resistor tuning network when said control signal tunes said transfer function of said resistor tuning network.
18. The method as claimed in
tuning out capacitative and resistor variations when said control signal tunes said transfer function of said resistor tuning network.
19. The method as claimed in
providing a tunable resistor in a master resistor tuning network, wherein said tunable resistor in said master resistor tuning network comprises said resistor tuning network;
providing at least one control signal from said master resistor tuning network to a plurality of electronic components on an integrated circuit chip, wherein each electronic component of said plurality of electronic components comprises a resistor tuning network capable of using said at least one control signal to provide a tunable resistor within said electronic component.
20. The method as claimed in
21. The method as claimed in
tuning all resistors on said integrated circuit that are capable of being tuned using said R-2R ladder network in said resistor tuning network.
22. The method as claimed in
operating said resistor tuning network as a tunable resistor that provides variable output values of resistance of said tunable resistor that range from said value of resistance of said tunable resistor minus five percent of said value of resistance of said tunable resistor to said value of resistance of said tunable resistor plus five percent of said value of resistance of said tunable resistor.
Descripción This patent application is related to and claims priority as a continuation-in-part of U.S. patent application Ser. No. 09/778,540 filed on Feb. 7, 2001 which is now U.S. Pat. No 6,573,811 for “RESISTOR TUNING NETWORK AND METHOD FOR MICROELECTRONIC RC-BASED FILTERS.” The present invention is also related to that disclosed in U.S. patent application Ser. No. 09/934,158 filed Aug. 21, 2001, entitled “EFFICIENT IMPLEMENTATION OP A COMPLEX FILTER WITH ON-CHIP RESISTOR TUNING;” The above applications are commonly assigned to the assignee of the present invention. The disclosures of these related patent applications are hereby incorporated by reference for all purposes as it fully set forth herein. The present invention relates generally to the tuning of a resistor in an electronic circuit, and, in particular, to the tuning of a resistor in an on-chip, microelectronic component such as an RC filter. Filtering is a fundamental signal processing tool used in almost all electronic systems. While some filtering functions can be performed in the digital domain, filtering in the analog domain is essential in countless applications where only analog techniques enable high-speed processing of small signal levels with the required resolution. Front-end processing in almost all electronic systems such as wireless and wireline communications, video, audio, imaging, etc. rely heavily on filtering in the analog domain. We have been witnessing in the last several decades that the cost and footprint of electronic systems are scaling down significantly as increasingly more functionality is integrated on a single chip of semiconductor. While microchip processing is extremely efficient in building a large number of devices on a microchip, analog processing still suffers from variations in component values from one fabrication run to another. Further limitations to analog processing accuracy come from the dependence of component parameters on temperature, which is becoming more and more costly to control as a result of larger scale integration. A widely recognized solution to this problem is the tuning of on-chip components until the error due to component variations becomes negligible. In a typical RC filter composed of amplifiers, resistors and capacitors, the accuracy of the filter transfer function is determined by the resistor and capacitor values. In general, either resistors or capacitors can be tuned to obtain the required overall transfer function. Tuning can be performed efficiently by switching small-valued components in or out of the circuit. As the dominant non-ideality of a reasonably-sized micro-switch is its parasitic resistance (up to very high frequencies), tuning of capacitors poses a difficulty as a result of an undesired resistance appearing in series with the capacitor to be tuned. Tuning of resistors, therefore, can be more effective in many realizations. If the resistor R However, in order to keep the gain constant, resistor R A typical example is a five thousand ohm (5 kΩ) resistor to be tuned to below one percent (1%) precision. This requires tuning resistors that are less than fifty ohms (50 Ω), which in turn requires a switch resistance on the order of ten ohms (10 Ω) or less. A switch with such a low on resistance requires a transistor that is several hundred times larger than a minimum geometry device. Note that, increased switch size, besides requiring more chip real estate, also exhibits higher parasitic capacitance along the signal path, and increased noise coupling through the substrate. The large spread of resistor values also limits the accuracy and matching between resistors. Small-valued resistors also require much more hand-tailoring in layout, as their aspect ratios turn out to be awkward, and parasitic contact resistances introduce considerable error to the overall resistance. Another difficulty is that different tuning resistor values are needed for each different resistor value to be tuned (so that the same relative accuracy can be maintained across all resistors). For example, fifty ohm (50 Ω) resistors are needed to tune a five thousand ohm (5 kΩ) resistance, whereas seventy five ohm (75 Ω) resistors would be needed to tune a seven thousand five hundred ohm (7.5 kΩ) resistor with the same relative increments. There is therefore a need in the art for an improved apparatus and method for tuning a resistor in an electronic circuit. In particular, there is a need in the art for an improved apparatus and method for tuning a resistor in an on-chip, microelectronic component such as an RC filter. To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a new and improved resistor tuning network that is particularly suitable for tuning microchip integrated resistors. According to one advantageous embodiment of the present invention, a resistor tuning network is provided that is capable of operating as a tunable resistor by providing variable output values of resistance. The resistor tuning network comprises a first resistor having a fixed value of resistance R A third resistor having a fixed value of resistance R This arrangement produces a resistor tuning network that exhibits good linearity in the resistor values with the switch positions, allowing the fine tuning of a large spread of resistor values. The resistor ladder network may be an R-2R ladder network. Because the switches in the R-2R ladder network are all in series with the same amount of resistance, i.e., 2R, they can be uniformly sized. In an advantageous embodiment of the invention, 2R is on the order of at least one thousand ohms (1 kilohm), so that the switch sizes can be kept small and so that the switch induced non-linearities can be kept negligible. Thus, this arrangement permits an effective resistor tuning network for an RC filter to be integrated on a single microchip. In one advantageous embodiment of the invention, the equivalent resistance REQ of the resistor tuning network is given by the following relationship:
According to another advantageous embodiment of the present invention, a method of operating a resistor tuning network as a tunable resistor is provided, which comprises the steps of: providing a first resistor having a fixed value of resistance R In one advantageous embodiment of the present invention, the resistor tuning network is integrated on a microchip on which an RC filter is built. In another advantageous embodiment of the present invention, the R-xR ladder network is an R-2R ladder network. By connecting a resistance in parallel with an R-2R ladder network, a resistor tuning network is provided that has good linearity in its tuning transfer function and allows a large spread of resistor values. With this arrangement, high tuning accuracy is achieved with a small spread in resistor values. Because the switches in the R-2R ladder are all in series with the same amount of resistance (i.e., 2R), they can be uniformly sized. By selecting 2R to be of the order of one thousand ohms (1 kilohm) or more, switch sizes can be made small, enabling the network to be integrated into a microelectronic chip or silicon chip. The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form. Before undertaking the Detailed Description of the Invention below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, it not most instances, such definitions apply to prior uses, as well as to future uses, of defined words and phrases. For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which: As illustrated in Ladder network As previously mentioned, when all the switches are closed in ladder network For fine tuning of resistors at different values, the non-linearity of this transfer curve poses severe difficulties. Tuning accuracy with respect to minimum switch steps becomes smaller and smaller as the equivalent resistor value increases. The linearity of the curve can be improved significantly by adding a resistance in parallel with the R-2R ladder. This is the purpose of the resistor R The transfer function of resistor tuning network Combining this expression with Equation 7 enables one to find the transfer function of resistor tuning network The series resistor R In designing an appropriate filter, first the value of the smallest resistor that is needed is calculated. The tunable network is then created where the value of resistor R The present invention allows one to tune the tunable resistor network with one control (e.g., a single knob) and move all of the different resistors by the same percentage at the same time. This feature maintains the resistor ratios. The present invention also allows one to tune out capacitive and resistor variation while maintaining the same transfer function. Now choose some exemplary values for resistor R The value of resistor R
The minimum equivalent resistor value of 3333 ohms for the binary setting “1111” (setting “16”) corresponds to a factor of 0.667. The factor of 0.667 will neutralize a process variation factor of 1.5 (or +50%). The maximum equivalent resistor value of 8888 ohms for the binary setting “0000” (setting “1”) corresponds to a factor of 1.778. The factor of 1.778 will neutralize a process variation factor of 0.652 (or −43.8%). To verify that resistor tuning network The value of resistor R
The minimum equivalent resistor value of 5333 ohms for the binary setting “1111” (setting “16”) corresponds to a factor of 0.667. The factor of 0.667 will neutralize a process variation factor of 1.5 (or +50%). The maximum equivalent resistor value of 14222 ohms for the binary setting “0000” (setting “1”) corresponds to a factor of 1.778. The factor of 1.778 will neutralize a process variation factor of 0.652 (or −43.8%). These values are the same values that were obtained in the case of the five thousand ohm (5.0 kilohm) resistor in the first example. Therefore, except for the different value for the R The resistor tuning network As previously mentioned, because resistor R By providing a first resistor with a fixed resistance R In this arrangement, all resistors to be tuned can use the same R-2R resistor ladder network Each tuning network in each block Although the present invention has been described in detail, those skilled in the art should understand that they can make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form. Citas de patentes
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